PVC pipe not to be used in compressed air systems

October 1990

The Department of Labor & Industries warned consumers and employers
in May 1988 that plastic-polyvinyl- chloride (PVC) pipe cannot be used
in compressed air piping systems without risk of explosion. By law, employers
must protect their workers by avoiding the use of unapproved PVC pipe
in such systems. Existing compressed air systems that use PVC piping
must be completely enclosed, buried or adequately guarded according to
specifications approved by a professional consulting engineer. Only Acrylonitrile-Butadiene-Styrene
(ABS) piping was approved for use with compressed air, provided it was
marked on the pipe as approved for compressed air supply.

In October 1989, the Plastics Pipe Institute (PPI) amended their original
recommendations for thermoplastic piping in the transport of compressed
air and other gases. WISHA's (Washington Industrial Safety and Health
Act) Division of Consultation and Compliance Services now will accept
thermoplastic compressed air piping that meets the following guidelines
(recommendation B, to the PPI 1972 recommendation):

"The Plastics Pipe Institute recommends that thermoplastic piping
intended for the transport of compressed air or other compressed gases
be buried or encased in shatter-resistant materials, unless thepiping
has been manufactured from materials which shall resist shatter-type
failures under the anticipated conditions. Specifically, above ground
installations of thermoplastic piping should only be made using products
which have been suitably evaluated and which are recommended by the manufacturer
for the particular intended service.

"It is recognized that while adequacy of strength is an important
element in the safety of a compressed gas piping system, consideration
must also be given to the nature of failure should accidental failure
occur, whatever its cause. Above-ground piping which fails by shattering
can present a serious hazard to personnel by the resultant flying shards,
or pipe fragments, which are rapidly propelled by the released energy
of the suddenly decompressing gas. Because the inclination of a material
to fail by shattering is determined not only by the nature of the material,
but by pressure, pipe and fitting dimensions, and by the nature of the
gas, the evaluation of shatter resistance should consider all these and
any other pertinent factors."

NOTICE TO EMPLOYEES: If you suspect that a pressurized PVC piping
hazard exists, bring it to the attention on your employer. If you do
not obtain satisfactory results, you may file a confidential complaint
with the Department of Labor & Industries. Complaints are investigated
promptly. Call the Department's toll free number at 1-800-423-7233.

NOTICE TO EMPLOYERS: If you have questions about the suitability
of a material for air system piping, call the Department of Labor & Industries Regional Office for a free consultation.